This invention relates to semiconductor device fabrication and processing, and, in particular, to a method and system for removing inorganic contamination from dielectric condensate precursor fluids, such as silicate esters, e.g. tetraethylorthosilicate (TEOS), by passing these fluids through columns of ion exchange resins to increase the purity of the fluids.
In the manufacture of modern integrated circuits, for example, contamination of the insulating interlevel dielectric layer material causes many problems and should be reduced as much as possible. Contamination is becoming an increasing problem, particularly as the complexity and density of integrated circuits increase and the feature sizes drop below about 0.25 xcexcm. Contamination may include contaminants, such as particulates, metallic ions, organic molecules, and other ionic species, that may be suspended or dissolved in the chemicals used for the manufacture of integrated circuits. Chemical processing utilized in the production of the integrated circuits often involves particle and metal removal steps followed by a drying step, interspersed with several rinsing steps.
Chemicals, such as dielectric condensate precursor fluids, are also used to form layers of insulating material between features of integrated circuits. Contaminants contained in such layers deposited on the surface of an integrated circuit substrate are particularly destructive when they are permanently included as part of the integrated circuit. These included contaminants may subsequently migrate to adjoining electrical device features and cause great damage to, or malfunction of, the integrated circuit and significantly reduce the product yield.
Dielectric condensate precursor fluids are typically applied as a fluid (gas, vapor, mist, or liquid) to the surface of an integrated circuit under vacuum and/or heat, and the fluid undergoes a conversion to a solid dielectric condensate. Conventional dielectric condensate precursor fluids include, but are not limited to silicate esters such as tetraethylorthosilicate (TEOS). Commercially available industrial, technical, or other grades of TEOS and other silicate esters typically include individual inorganic contaminants in concentrations up to about 10,000 parts per billion (ppb). Thus, for semiconductor manufacturing and certain other processes, the commercial manufacturer is requested, therefore, to further purify the silicate esters or other dielectric condensate precursor fluids.
Current methods for the purification of TEOS and related organic silicate fluids employ sequential fractional distillation at atmospheric or reduced pressures and higher temperatures. These methods suffer from several drawbacks that include the inability to remove significant amounts of boron and chloride ions, the facilitation of undesirable side reactions at operational temperatures, and the costly safeguards needed for distillation of flammable and hazardous materials.
A safer, less expensive, and more effective method of purifying TEOS, silicate esters, and other dielectric condensate precursor fluids is, therefore, desirable.
An object of the present invention is, therefore, to provide a system or method for removing contaminants from silicate esters or other dielectric condensate precursor fluids.
The present invention presents a method that employs ion exchange resins to remove metal and other contaminants from dielectric condensate precursor fluids and silicate esters, such as TEOS and to avoid certain drawbacks of the current distillation techniques. Ion exchange resin is currently used for the removal of contaminants from water and a few other chemicals, such as citric acid. The ion exchange resin beads have a positive or negative charge which attract contaminants of the opposite charge. Macroporous ion exchange resins additionally have numerous crevices at the surface of each resin bead. These crevices function to physically trap contaminant molecules, creating a molecular sieve effect that can capture contaminants even when the ion exchange resin is surrounded by an organic fluid.
The present invention includes, therefore, selecting or modifying ion exchange resin to be appropriate for the process, such as by converting the cations to hydrogen and the anions to hydroxide; drying or eliminating water from the ion exchange resin, such as by rinsing the resin with an evaporative alcohol; flushing the ion exchange tanks and associated chemical lines with the fluid to be purified; recirculating the commercial fluid feedstock through tanks of ion exchange resin one or several times to achieve optimum removal of contaminants; and delivering the purified fluid into a closed container to prevent subsequent contamination. The process may be carried out at room temperature and pressure.
Skilled persons will also appreciate that the present invention can be employed in the manufacturing of extremely pure silicate powders or slurries that can, for example, be used to polish silicon wafers.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.